有一列数a1,a2,a3,.,an,从第二个数开始,每一个数都等于1于它前面的数的倒数的差,若a1=2,则a2009=

2个回答

  • a[n] = 1 - 1/a[n-1]

    = (a[n-1]-1)/a[n-1]

    a[n+1] = 1 - 1/a[n]

    = 1 - a[n-1]/(a[n-1]-1)

    = - 1/(a[n-1]-1)

    a[n+2] = 1 - 1/a[n+1]

    = a[n-1].

    ∴ a[n+3] = a[n]

    ∴ a[2009] = a[2] = 1 - 1/a[1] = 1/2.

    应该没有错吧``` .